IDENTIFICATION AND CHARACTERIZATION OF MONOCLONAL-ANTIBODIES SPECIFICFOR POLYMORPHIC ANTIGENIC DETERMINANTS WITHIN THE V2 REGION OF THE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 ENVELOPE GLYCOPROTEIN

We have identified six monoclonal antibodies (MAbs) mapping to both li near and conformation-dependent epitopes within the V2 region of the h uman immunodeficiency virus type 1 clone HXB10. Three of the MAbs (12b , 66c, and 66a) were able to neutralize the molecular clones HXB10 and HXB2, with titers in the range of 9.5 to 20.0 mu g/ml. MAbs mapping t o the crown of the V2 loop (12b, 60b, and 74) bound poorly to cell sur face-expressed oligomeric gp120, suggesting an;explanation for the poo r or negligible neutralizing activity of MAbs to this region. In contr ast, MAbs 12b and 60b demonstrated good reactivity with recombinant gp 120 in an enzyme-linked immunosorbent assay format, suggesting differe ntial epitope exposure between the recombinant and native forms of gp1 20. Cross-competition analysis of these MAbs and additional V1V2 MAbs for gp120 binding enabled us td assign the MAbs to six groups (A to F) . Selection of neutralization escape mutants with MAbs 10/76b and 11/6 8b, belonging to nonoverlapping competition groups, identified amino a cid changes at residues 165 (I to T) and 185 (D to N), respectively. I nterestingly, these escape variants remained sensitive to neutralizati on by the nonselecting V2 MAbs. All MAbs demonstrated good recognition of IIIB viral gp120 yet failed to neutralize nonclonal stocks of IIIB . In addition, MAbs 12b and 62c bound MN and RF viral gp120, respectiv ely, yet failed to neutralize the respective isolates. Cloning and exp ression of a library of gp120 and V1V2 fragments from IIIB-, MN-, and RF-infected H9 cultures identified a number of polymorphic sites, resu lting in antigenic variation and subsequent loss of V2 MAb recognition . In contrast, the V3 region from the clones of the same isolates show ed no amino acid changes, suggesting that the V2 region is polymorphic in long-term-passaged laboratory isolates and may account for the red uced antibody recognition observed.